A tunnel can be lined with concrete behind a tunnel excavator having a shield advanced with the excavator head in which the concrete is forced between the surrounding subterranean geological structure and the inner tunnel-lining form through a form front which rides sealingly on the outer surface of an inner tunnel-lining form and on the inner surface of the shield.
The form front moves forward relative to the inner tunnel-lining form longitudinally and generally also relative to the shield. The form front is thus movable forward simultaneously with concrete feed behind the form front, balancing the friction forces between the form front and the shield and the inner tunnel-lining form.
An apparatus for carrying out this process is known in which the form front has an outer seal contacting on the inner surface of the shield and an inner seal contacting on the outer surface of the inner tunnel-lining form, is provided with a movable concrete feed hose connected to a concrete pump, and is provided with an adjustable hydraulic spring device balancing the friction forces. A displacement measuring device which is an input element of a control device is associated with the form front and the shield.
Among the known features of this process as described in German Pat. No. 34 06 980 is in particular an adjustment of the hydraulic spring device.
A control device acts only to keep the form front within a predetermined distance from the shield or excavator head, has a piston-cylinder device by which the shield is coupled to a drive unit of the tunnel excavator, and has a concrete pump as a control element.
These features do not meet the requirements of the process. Experience with tunnel excavators in the diameter range of 6 to 7 meters has shown that the required balancing forces can fluctuate between 400 and 1400 kN. This leads to correspondingly large fluctuations of the concrete pressure required for the forward motion of the form front with corresponding negative consequences for the quality of the tunnel lining, especially in loose earth and beneath the water table.
To maintain a satisfactory quality concrete lining the ensuing pressure fluctuations must be reduced. The concrete pressure in the form must be kept above the rising earth and water pressure and within a safe range.